Hard disk drives (HDD) are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model includes a storage disk or hard disk that spins at a designed rotational speed. An actuator arm with a suspended slider is utilized to reach out over the disk. The slider is coupled with a suspension that supports both the body of the slider and a head assembly that has a magnetic read/write transducer or head or heads for reading/writing information to or from a location on the disk. The complete head assembly, e.g., the suspension, slider, and head, is called a head gimbal assembly (HGA).
A typical HDD uses the actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read from the location. Within most HDDs, the magnetic read/write head is mounted on a slider. The slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive. The slider is aerodynamically shaped to establish an air lubrication film in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
The reading or writing of data is performed in accordance with a write command and a read command transferred from a host system. The hard disk drive re-orders a command queue as one of the performance improving techniques. That is, the command queue of write commands and read commands transferred sequentially from the host system is re-ordered so that the latency required to execute the writing or reading command may be minimized.
Various methods for re-ordering the command queue in the hard disk drive have been already offered. They are roughly classified into a method for improving the I/O throughput (amount of work performed over a period of time) and a method for preventing the time-out of command caused by re-ordering the command. And the method for improving the I/O throughput is further classified into a case where the seek time is longer than the rotational latency and a case where the seek time is almost equivalent to the rotational latency.
All the above re-ordering techniques are implemented in one way or the other to improve performance and to save power. The premium for saving power consumption in hard disk drive have transcended across the various platforms (e.g., from mobile computers to server computer products). Conventional methods for power saving or reduction include JIT (Just In Time seek technology). This method delays the seek time by an amount of the rotational latency to make power save and enhance performance. Other conventional methods involve directly switching the seek method (including servo parameters) between a performance mode and a silent mode.
These methods are very effective but require to have parameters for the servo system duplicated, and therefore have a significant drawback of taking a great burden on the development because it must be checked that the seek is normally made for all combinations of the seek distance and the latency.